HIGH TEMPERATURE X-RAY DIFFRACTION STUDY OF THE MELTING SEQUENCE OF THE 2223 PHASE IN THE Bi-Sr-Ca-Cu-O SYSTEM. C. Park, W. Wong-Ng^*, L. P. Cook^*, R. L. Snyder, P. V. P. S. S. Sastry, A. R. West^**, Alfred University, Alfred, NY, ^*Ceramics Division, National Institute of Standards and Technology, Gaithersburg, MD, ^**Aberdeen University, Aberdeen, Scotland

Unlike the Pb-doped 2223 ((Bi,Pb):Sr:Ca:Cu) phase, relatively little data has been reported on the characterization and applications of the Pb-free 2223 phase. This is probably due to the difficulty of preparing high purity material. We have successfully prepared a mostly single phase 2223 material. Since melting information is important for processing, the goal of this paper is to use the in-situ high temperature x-ray technique (in combination with the thermal differential analysis (DTA) and quantitative SEM/EDS) to investigate the melting sequence of the 2223 phase.

It was found that the melting sequence of the 2223 phase is similar to the 2212 phase in that the primary crystals are calcium strontium cuprates and calcium strontium oxides. In the Ag-free material, at least two phases were observed during the melting process. At around 890deg., the (Ca,Sr)₂CuO₃ appeared and at around 950deg.C, the (Ca,Sr)O phase was formed. When Ag powder was well mixed with the the sample, the melting temperature of the 2223 phase was lowered by about 20deg.C and at least 3 alkaline-earth phases were observed during melting. At around 870deg.C (Ca,Sr)CuO₂ was observed first followed by the appearance of (Ca,Sr)₂CuO₃ at ~ 890deg.C and (Ca,Sr)O at about 950deg.C.